In relation to bearing devices for rotatably supporting a rotational shaft, a floating bush bearing device is known, which includes a floating bush having a cylindrical shape and including a bearing hole into which a rotational shaft can be inserted (see Patent Document 1, for instance). Such a floating bush bearing device supplies a gap between a floating bush and a rotational shaft with lubricant oil to form an oil film, and rotatably supports the rotational shaft with the oil film formed in the gap.
Furthermore, in the floating bush bearing device disclosed in Patent Document 1, the circularity of the inner peripheral surface of the floating bush is changed into a polygonal shape to enhance the centering effect, thus improving the oscillation stability.